2018 ASHS Annual Conference

Sweet basil (Ocimum basilicum) is widely used as a culinary herb and medicinal plant due to its unique aromatic flavor and relatively high content of phenolic compound. Effects of light quality on the growth and nutritional quality of green basil ‘Improved Genovese Compact’ and purple basil ‘Red Rubin’ were evaluated. Uniform basil seedlings with one pair of fully-expanded true leaves were transplanted and moved into a walk-in growth room for six light quality treatments, including two full spectrum light treatments (white fluorescent lamp, WFL; and white light-emitting diode lamp, WLED) and four combinations of red and blue LED light treatments with different red: blue (R:B) ratios (R:B=1.18, R1B1; R:B=3.44, R3B1; R:B=6.39, R6B1; R:B=7.84, R8B1). All plants were sub-irrigated as needed using a nutrient solution with electrical conductivity of 2.0 dS·m^-1 and pH of 6.0, and the room temperature was maintained at 23.9/21.3ºC day/night. The results showed that the gas exchange rate, namely, net photosynthetic rate, transpiration rate, and stomatal conductance of green and purple basil plants were the highest under R1B1 treatment, and the net photosynthetic rate of green basil plants were 57% higher than purple basil plants, whereas its transpiration rate was 76% lower. The total leaf area of purple basil plants was the highest under R8B1, followed by R6B1 and R3B1, and was the lowest under WLED, but no difference was observed on total leaf area of green basil plants among six light quality treatments. The shoot FW of green and purple basil plants were higher under combinations of red and blue LED light treatments compared with full spectrum light treatments and increased with increasing R: B ratios. The anthocyanin concentration of green basil plants was decreased with increasing R: B ratios, and no difference was observed between R6B1 and R8B1 treatments. The total phenolics and flavonoid concentration of green basil plants were both the highest under R3B1 treatment. Considering the yield and nutritional quality of basil plants, combinations of red and blue LEDs with red light percentage higher than 75% was recommended for green and purple basil production under controlled environment.